I have a older house with iron waste pipes. The upstairs clothes
washer two floors up is a front loader maytag. It drains water down a
2 or 2 1/2 inch pipe . The sink on the botton floor that backs up is
on a run two feet from this verticle and 4 feet from the bottom of 7ft
horrizontal run then to 4inch out the house. When I say backs up, it
bubble a small amount into the sink. Once it did over flow and then I
snaked the down side of this run but never 100%. Is there a one way
check valve that can be spliced in just on the other side of the
clean-out?